It is well known to include reflectors in directional antennas in order to shape the antenna radiation pattern. The reflectors also eliminate signal transmissions in directions other than the selected, or principal, direction which may interfere with the signal transmissions of nearby antennas.
Various parts of an antenna structure, for example, an antenna support, may act as unintended and unwanted reflectors, reflecting signals away from the principal direction. These reflected signals may adversely affect the transmission in the principal direction and/or interfere with nearby transmissions. In order to minimize such reflections, many antenna systems include absorbers. The absorbers, or signal attenuators, are placed over or around the unwanted reflectors. When the antenna transmits a signal, the portion of the signal which would otherwise be reflected by the unwanted reflector is instead "absorbed" or largely attenuated by the absorber. The unwanted reflection is thus relatively weak and less likely to interfere with the transmissions of that or any nearby antenna.
Antenna reflectors reflect any signal they receive, not just the signals transmitted by the associated antenna. Typically, such reflections are ignored because they do not interfere with the signals transmitted by the antenna. For example, reflectors included in antennas designed for low frequency signal transmission also reflect higher frequency radar signals. If the antennas are used on vehicles for which a low radar profile is desired such reflections cannot be ignored, because they increase the radar cross section of the vehicle.
Absorbers can be used to attenuate the signals reflected by the portions of the vehicle which are not intentionally used as antenna reflectors. However, absorbers can not be used to attenuate the signals reflected by the antenna reflectors without rendering the antenna virtually useless. What is needed is a mechanism which enables an antenna reflector to reflect signals within the operative frequency range of the antenna and attenuate signals outside that range.